In-Situ Metallography
As an NDE method, Field metallography is widely used in microstructure analysis for large structures that cannot be easily moved or for which destructive sample preparation is difficult or not permissible. Such large structures include storage tanks, piping systems, large machinery, boilers or aging high temp pressure vessels. In-situ Metallography allows for quick on-site evaluation of a component’s metallurgical and heat treatment condition.
Grain size and grain flow, carbides, cracks and undesired phases can be readily identified with our portable machinery without a reduction in quality compared to in-lab analysis. In fact, field metallography is the most accurate way to identify high temperature hydrogen attack (HTHA) and early stage Stress Corrosion Cracking (SCC). It is a powerful tool in assisting materials identification, health monitoring, remaining life assessments, or failure analysis.
On-site metallurgical sample preparation poses more difficulties in many cases as inappropriate polishing and etching procedures might introduce artifacts which complicate actual microstructure interpretation. PMI specialists has a highly skilled and well-equipped team to perform field metallography.
The normal procedure is as follows: portable grinder and polisher are used for on-site sample preparation. Then a field microscope is used to examine the quality of the polish. After a satisfactory finishing is achieved, a compatible chemical etchant is used to reveal the microstructure of the polished spot. If desired, electrochemical etching can also be performed.
If needed, we can even take micrographs at 1000x magnification through proprietary techniques, which nobody else in the world has attempted, much less achieved. If even greater resolution is required, PMI specialists can perform field replica service using acetate film or silicone based resin . Replicas can be viewed and analyzed by either optical or electron microscope in the lab.
The following micrographs are some examples we took from the field at 100x or 400x magnification this year.
